Smelting is a common method for recovering the desired metal value from sulfidic ores. During the smelting process, the sulfur in the ore is oxidized, resulting in an exothermic reaction, whereby the heat generated is sufficient to melt the metal without the need for an external heat source. Typically, a carbonaceous reducing agent, such as coke, is employed in the reaction.
Reverberatory smelters, sometimes called “copolas” are commonly used. The fuel and metal ore charge are usually fed separately. In the first step, two liquids are formed: one is an oxide slag containing the impurities, and the other is a sulfide “matte” containing the valuable metal sulfide and some impurities. Fuel is burned at one end of the furnace, and the heat melts the dry sulfide concentrate (usually after partial roasting) which is fed through the openings in the roof of the furnace. The slag floats on the top of the heavier “matte” and is removed or rejected. The sulfide matte then is forwarded to a converter.
Metal production during the smelting operation is limited by the upper temperature limitations of the smelting furnace. Due to the exothermic nature of the pyrometallurgical reduction, adding additional metal sulfide has the same effect as adding more fuel. In order to increase production, smelters can benefit from smelting ores with increased surface moisture since the moisture will evaporate, reducing the temperature of the upper furnace, and thereby allowing more ore to be fed to the furnace, resulting in an increase in metal production.
While adding moisture to a sulfidic ore prior to smelting provides benefit, the amount of moisture added is limited due to problems that may be associated with increasing ore moisture content, such as caking and clogging of conveyor belts and other conventional ore transport means.